drm: Add CrtcGetSequence and CrtcQueueSequence IOCTLs [v2]

These provide a crtc-id based interface to get the current sequence
(frame) number and to queue an event to be delivered at a specific sequence.

v2: Remove FIRST_PIXEL_OUT flag. This has been removed from the
    proposed kernel API

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>